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      <title>你以为你懂InnoDB锁机制 - 交互式测验</title>
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              <h1>你以为你懂InnoDB锁机制 - 交互式测验</h1>
              <p>检验你对文档内容的理解程度</p>
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        const quizData = [
  {
    "question": "根据文档，间隙锁（Gap Lock）被引入InnoDB的主要目的是什么？",
    "options": [
      "只锁定正在被修改的单条记录，实现最细粒度的并发控制。",
      "锁定两个现有记录之间的“空隙”，防止其他事务在这个区间内插入新数据，从而避免幻读。",
      "在批量更新时将整个数据表锁定，以保证操作的原子性。",
      "作为记录锁的备用方案，在记录锁失败时启用。"
    ],
    "correctAnswerIndex": 1,
    "explanation": "间隙锁的核心作用是锁定一个范围，但这个范围里并不包含实际存在的记录。它的设计目标是防止其他事务在这个“间隙”中插入新的记录，这在可重复读（REPEATABLE-READ）隔离级别下对于防止“幻读”至关重要。就像文档中比喻的，在两个已停放的车位之间拉上警戒线。",
    "source": "文档中「二、比Java的synchronized复杂10倍」下的「2. 间隙锁（Gap Lock）」部分",
    "hint": "思考一下这种锁的命名——“间隙”，它锁定的不是实体记录，而是记录之间的什么？"
  },
  {
    "question": "文档描述了一个生产事故：一个批量更新操作因范围查询导致了大范围锁定。这揭示了InnoDB哪种锁机制的行为特性？",
    "options": [
      "当WHERE子句中的条件列没有索引时，行锁会自动升级为表锁。",
      "当更新的数据量过大时，InnoDB会自动放弃行锁，转而使用表锁以节省资源。",
      "当WHERE子句中使用范围查询时，InnoDB会使用间隙锁或临键锁来锁定记录及记录间的空隙，导致锁定范围扩大。",
      "任何UPDATE语句在默认情况下都会先锁定整个表，然后再释放未匹配的行。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "文档开篇的案例明确指出，通过 `SHOW ENGINE INNODB STATUS` 发现出现了间隙锁。这是因为 `WHERE` 条件使用了范围查询（如 `amount > 100`），InnoDB为了保证事务隔离性（尤其是在默认的RR级别下防止幻读），会锁住满足条件的记录之间不存在的区间，从而导致锁定范围超出预期。",
    "source": "文档中「一、什么是行级锁？」部分",
    "hint": "回顾文档开头的那个“骨感”的现实案例，是什么样的查询条件导致了整个表被锁住？"
  },
  {
    "question": "根据文档对临键锁（Next-Key Lock）的定义，以下哪个描述是正确的？",
    "options": [
      "它是一种比记录锁更细粒度的锁，只锁定记录的一部分。",
      "它是专门用于解决死锁问题的一种乐观锁。",
      "它是记录锁（Record Lock）和间隙锁（Gap Lock）的组合体。",
      "它是共享锁（S锁）和排他锁（X锁）的另一种称呼。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "文档中明确定义，临键锁是记录锁和间隙锁的组合。它不仅会锁住查询到的记录本身（记录锁的功能），还会锁住该记录与前一条记录之间的间隙（间隙锁的功能）。这是InnoDB在可重复读隔离级别下的默认锁模式。",
    "source": "文档中「二、比Java的synchronized复杂10倍」下的「3. 临键锁（Next-Key Lock）」部分",
    "hint": "文档中直接说明了临键锁是一个“组合”，是哪两种锁的结合？"
  },
  {
    "question": "在“我踩过的五个深坑”一节中，`WHERE varchar_col = 123` 这样的SQL语句为什么会导致性能灾难？",
    "options": [
      "因为发生了隐式类型转换，导致`varchar_col`列上的索引失效，从而引发全表扫描。",
      "因为在WHERE子句中直接使用数字字面量会使查询缓存失效。",
      "因为MySQL的优化器无法处理`varchar`类型和`int`类型的等值比较。",
      "因为这种查询会触发一个特殊的、锁定范围非常大的“数字范围锁”。"
    ],
    "correctAnswerIndex": 0,
    "explanation": "该案例的核心问题在于数据库的隐式转换。当字符串类型的列（`varchar_col`）与数字类型的值（`123`）进行比较时，MySQL为了使比较能够进行，会将列中的所有值都转换为数字。这个转换操作是在函数内部完成的，导致无法使用该列上的索引，最终退化为效率极低的全表扫描。",
    "source": "文档中「六、我踩过的五个深坑」部分的「3. 隐式转换索引失效」",
    "hint": "当列的数据类型和查询值的数据类型不匹配时，数据库会做什么来让它们可以比较？这个操作对索引的使用有什么影响？"
  },
  {
    "question": "根据文档中的锁兼容性表，当一个事务已经对某资源持有了X锁（排他锁）时，另一个事务尝试对同一资源申请加锁，会发生什么情况？",
    "options": [
      "可以成功申请S锁（共享锁），但不能申请X锁。",
      "可以成功申请间隙锁。",
      "无论是申请X锁、S锁还是间隙锁，都会被阻塞。",
      "只能成功申请S锁，且必须等待当前X锁释放。"
    ],
    "correctAnswerIndex": 2,
    "explanation": "从文档提供的兼容性矩阵中可以看出，X锁所在的第一行和第一列，与所有其他锁（包括X锁、S锁和间隙锁）的交叉点都是 `❌`（不兼容）。这意味着排他锁具有完全的排他性，一旦被持有，任何其他类型的锁请求都会被阻塞，直到该X锁被释放。",
    "source": "文档中「三、数据库版的锁」部分的锁兼容性表",
    "hint": "请查阅文档中的锁兼容性表格，观察“X锁”所在的那一行，它与其他所有锁的关系是怎样的？"
  },
  {
    "question": "如果你希望在一个事务中读取某一行数据，并确保在你事务结束前，其他任何事务都不能修改这一行（即加上排他锁），你应该使用哪条SQL语句？",
    "options": [
      "`SELECT * FROM table WHERE id=1 LOCK IN SHARE MODE;`",
      "`SELECT * FROM table WHERE id=1;`",
      "`SELECT * FROM table WHERE id=1 FOR UPDATE;`",
      "`LOCK TABLE table WRITE;`"
    ],
    "correctAnswerIndex": 2,
    "explanation": "文档中明确指出，`SELECT ... FOR UPDATE` 会为查询到的行加上一个排他锁（X锁）。这个锁会阻止其他事务对该行进行任何更新（加X锁）或加共享锁（`LOCK IN SHARE MODE`）的操作，从而达到了在当前事务中独占该行的目的。而`LOCK IN SHARE MODE`只加S锁，允许多个事务同时读取。",
    "source": "文档中「二、比Java的synchronized复杂10倍」下的「1. 记录锁（Record Lock）」部分",
    "hint": "文档中介绍了两种手动为SELECT语句加锁的SQL语法，哪一种对应的是排他锁（X锁）？"
  },
  {
    "question": "当数据库发生死锁时，根据文档推荐，首选的、能够提供最详细死锁信息的诊断命令是什么？",
    "options": [
      "`SHOW PROCESSLIST;`",
      "`SHOW ENGINE INNODB STATUS;`",
      "`SELECT * FROM information_schema.INNODB_TRX;`",
      "`EXPLAIN [SQL语句]`"
    ],
    "correctAnswerIndex": 1,
    "explanation": "文档中演示了如何通过 `SHOW ENGINE INNODB STATUS` 命令来查看 `LATEST DETECTED DEADLOCK` 部分。这部分信息包含了构成死锁的事务、它们正在等待的锁、持有的锁以及它们正在执行的SQL语句，是分析和解决死锁问题的最直接、最核心的工具。",
    "source": "文档中「四、如何解决死锁」部分",
    "hint": "文档中给出了一个详细的死锁日志示例，这个示例是通过哪个命令获取的？"
  }
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            const skippedCount = totalQuestions - answeredCount;
            const accuracy = totalQuestions > 0 ? Math.round((correctCount / totalQuestions) * 100) : 0;
            const errorRate = totalQuestions > 0 ? Math.round((wrongCount / totalQuestions) * 100) : 0;

            const finalScoreHtml =
                '<div class="final-score-container">' +
                '<h2>答题报告</h2>' +
                '<div class="score-summary">' +
                '<div class="score-card">' +
                '<h3>得分</h3>' +
                '<p>' + correctCount + ' / ' + totalQuestions + '</p>' +
                '</div>' +
                '<div class="score-card">' +
                '<h3>正确率</h3>' +
                '<p>' + accuracy + '%</p>' +
                '</div>' +
                '<div class="score-card">' +
                '<h3>错误率</h3>' +
                '<p>' + errorRate + '%</p>' +
                '</div>' +
                '<div class="score-card score-details">' +
                '<table>' +
                '<tr><td>正确</td><td>' + correctCount + '</td></tr>' +
                '<tr><td>错误</td><td>' + wrongCount + '</td></tr>' +
                '<tr><td>未答</td><td>' + skippedCount + '</td></tr>' +
                '</table>' +
                '</div>' +
                '</div>' +
                '<div class="report-actions">' +
                '<button id="review-btn">回顾测验</button>' +
                '<button class="primary" onclick="location.reload()">再试一次</button>' +
                '</div>' +
                '</div>';

            let reportEl = document.querySelector('.final-score-container');
            if (reportEl) {
                reportEl.remove();
            }
            quizContentEl.insertAdjacentHTML('beforeend', finalScoreHtml);
            document.getElementById('review-btn').addEventListener('click', reviewQuiz);
        }

        function reviewQuiz() {
            const reportEl = document.querySelector('.final-score-container');
            if (reportEl) {
                reportEl.remove();
            }

            document.querySelector('.quiz-body').style.display = 'block';
            document.getElementById('quiz-footer').style.display = 'flex';
            
            currentQuestionIndex = 0;
            loadQuestion();
            updateNavigationButtons(); // Ensure nav buttons are correctly displayed
        }

        // Event Delegation for options
        optionsListEl.addEventListener('click', (event) => {
            if (event.target && event.target.matches('li.option-item')) {
                // Check if the question has already been answered
                if (userAnswers[currentQuestionIndex] === null) {
                    const selectedIndex = parseInt(event.target.dataset.index, 10);
                    selectOption(selectedIndex);
                }
            }
        });

        prevBtn.addEventListener('click', goToPreviousQuestion);
        nextBtn.addEventListener('click', goToNextQuestion);
        hintBtn.addEventListener('click', showHint);
        
        // 初始加载
        loadQuestion();
      </script>
    </body>
    </html>
  